Electromagnetic switch and system therefor



Aug. 22, 1939. v c. L. PERRY 2,170,694

ELECTROIAGNETIG SWITCH AND SYSTEM THEREFOR Fi1ed Oct. 1, 1937 HATER/ALInventor.

IBWIANENTLY HAGNETIZABLE Charles L. P rry.

b if? y Hi Attorhey.

' a portion hereinafter called 5g rial of high magnetic Patented Aug.22, 1939 UNITED STATES PATENT orrica 7 2,170,667: I I nnacmomcnm'rc'swrron AND srs'ram mam--03 GharlesL. Perry, Schenectady, N.

General Electric New York Y., asngnor to Company, a corporation of7Claims.

My invention relates to electromagnetically operated switches and hasfor its object a simple and reliable electromagnetic switch and systemtherefor which is held of permanently magnetizable material, and whichmay be opened and closed by operating coils or opened an overload by. acurrentresponsive coil.

In one form of my invention I provide an electromagnet for closing theswitch, this magnet-being provided with an armature connected to theswitch and a magnet frame member provided with the holding magnet. madeof a material having a highcoercive force which holds residual flux whenmagnetized so as to hold the switch closed. provided for. attracting thearmature to close the switch. A second operating coil connected tooppose the holding magnet is provided for releasing the armature toallow the switch to open, and if-desired, one or more additional coilsalso opposing or neutralizing the holding magnet may be provided andenergized in response to the current in the switch so as to open theswitch on overload.

For a more complete understanding of my invention, reference should behad to the accompanying drawing, Fig. 1 of which is a side elevationview of a switch embodying my invention; while Fig. 2 is a diagram .ofacontrol system for an electric motor utilizing this switch.

Referring to the drawing, in carrying out my invention, I provide apivoted armature l0 mounted rigidly on a pivot shaft I I together with amagnet frame member l2 .of soft magnet core iron and a plurality ofoperating coils l3, l4, l5 and I6 provided with an axially extendingcore II. This core I] which forms a field structure with the member l2has a relatively short circular or disk-shaped portion [8, forming aholding magnet, made of a suitable material having a high coerciveforce, and a relatively long portion made of soft magnet core ironconstructed in two parts, I! and 20. Although the two parts, I! and 20,could be made as one, the provision of the relatively short section 20makes its possible to leave out this section in the event that theportion I9 is long enough to form,.with the portion II a core of thedesired length. The armature II is providedavith a member 20a made ofmagnet core iron extending across the ends of the core I! and the framemember 2! when the armature is in attracted position as shown in Fig. 1to complete a magnetic flux path between them.

The portion I8 is preferably made of a mate'- closedby a magnet made An,operating coil is,

coercive force consisting 20% nickel, and 5% cobalt, the balance beingiron.

As shown, the core portion 1 8 forming the holding magnet has a lengthin the direction of the '7 lines of magnetic force, i. e. axially of thecoils H to IE, which is only a fraction of its diameter as shown inFig. 1. I have found that this construction provides for much greatermagnetic pull on thu armature per unit weight of holding magnet materialthan a construction of smaller diameter and greater axial length. Forexample, a core of this material, four and one-quarter inches (4%") longby two inches (2") in diameter, in one device gave less pull on thearmature than a. core one inch (1") long with a diameter of two andone-quarter inches (2%") the remainder of the core in each case being ofsoft steel. Another advantage of the axially short holding magnet isthatfewer turns in the operating coil are required to pick up the armature.

. It will be understood that the movably mounted contacts of the switchare mechanically connected to the armature I0. As shown in Fig. 2, thethree pivotally mounted contact arms 2| are secured to an extension 22of the pivot shaft II to which the armature I0 is secured. These movablecontacts arms, which form with their stationary contacts a three poleswitch, are biased to their open circuit positions as by a suitablespring as shown or by the weight of the armature, the armature whenreleased coming to rest against a stop 23 provided for it.

In Fig. 2, I have shown a control system in which the switch of Fig. 1is embodied, the switch being connected to control the supply of currentfrom suitable three phase mains 24 to a three phase motor 25. In thissystem the coil It serves as an operating coil to pick up the armatureand move it to its attracted position.

The coil I5 serves as an opening coil. This coil when energized producesa flux inopposition to the flux of the holding magnet thus neutralizingthe magnet and releasing the armature which thereupon drops to move thecontact arms 2| to their open circuit positions, as shown in Fig. 2.

The coils l3 and N are connected respectively in two of the alternatingcurrent supply lines running to the electric motor 25. These coils areenergized in response to the current passing through the switch,i. e.the current in the motor 25, and upon the occurrence of a predeterminedswitch arms 2i.

- released and its upper pair of contacts being"- closed, the relay coil28 is again energized as pre-'" 70' current in these coils, neutralizethe permanent magnet and allow the armature to drop and open the switch.

I have provided direct current supply mains 25 and 21 for energizing thecoils i5 and I5, and also for energizing the coil 28 of a relay providedwith bridging switch contacts 29 and 30. This relay is biased to itsopen position, as shown by gravity, and when the switch arms 2| are intheir open circuit positions, as shown, the coil 28 is normallyenergized. Its circuit leads from main 26 through a normally closedtwo-way push-button 3|, condoctor 32, coil 28, and conductor 33 to themain 21.

- Two interlock switches 34 and 35 are mounted on the frame member l2with their operating rod 36 in position to be engaged by an extensionill on the end of the armature 3 when the armature reaches its attractedposition. The switch 35 is normally closed whereas the switch 3:3isnormally opened as indicated in Fig. 2, and the armature when pickedup, closes the switch 34 and opens the switch 35, the switches beingbiased by a spring 31.

When it is desired to start the motor, the push? button 3| is pressed toits lowermost position. This first opens the circuit through theuppermost contact of. the push-button 3| whereby the circuit for thecoil 28 is transferred through the switches 29' and 35. This circuitleads from the main 26 through the conductor 38, the switch 29,conductor 39, switch 35, coil 23, and the conductor 33 to the supplymain 27. When a circuit through the lower contact of the push-button 3iis completed, a circuit is established for the coil it which picks upthe armature H3, closing the This circuit leads from the supply main 26through conductor 38, switch 29, conductor 39, the lower pair ofcontacts of the push-button 3|, through the switch 30, conductor 40, andthe. coil Hi to the supply main 2?. When the armature opens the switch35, the circuit of the coil 28 through this switch is opened whereuponthe switches 29 and 38 drop open, thereby opening the circuit for thecoil it. The switch is now closed and the motor 25 energized, thearmature l being held in its closed position by the holding magnet IB.

Should it now be desired to open the switch arms 2|, the push-button llis depressed whereby the coil i is energized. This circuit leads fromthe main 26 through the button M, the switch 36' which is then closed,the conductor 42, and the coil Hi to the main 2?.

In the event of an excessive load on the motor, the coils l3 and i4produce jointly a magnetic flux suflicient to neutralize the holdingmagnet whereupon the armature Ill drops to open the switch arms 2|.fective to open the switch despite the fact that they are energized withalternating current, for the reason that the alternating flux of thesecoils neutralizes the residual magnetism of the holding magnet.

When the armature is released, the switch 34 opens and switch 35 closesin accordance with their biases and the push-button 3| having beenviously described. The push-button 3| must now lie-depressed again'toenergize the coil IS in order that the switch arms 2| may again be movedto' their closed positions. This interlocking arrangement preventsrepeated opening and closing of the switch-in the event that an overloadoc- The coils l3 and M are ef-- cars at the instant the switch closesand before the push-button 3| is released. Even though .theif.

interlock switch 35 is closed'when the armature l0 isreleased, thearmature cannot be picked up again because the relay switches 29 and 3Bare both open thus maintaining open circuits for the coils i6 and 28. Aspreviously indicated, to reclose the switch the button 3| must bereleased to close the relay switches 29 and 30, and then pressed.

The energization of the coils l3, It and id to open the switchdemagnetizes the holding magnet |8 to a very great extent so that itcannot at tract the armature with suficient force to hold the switchclosed. When the pick-up coil it is energized, however, the holdingmagnet is again magnetized and holds the switch closed. A property ofthis material is that-after once being magnetized, it is very readilyre-magnetized. The pick-up coil it must be energized with direct currentin order that the holding magnet may be re-magnetized, while the openingcoils l3, M and I5 may be energized with either alternating current ordirect current. As shown, the coil i5 is energized with direct currentand in that case it must be energized in such direction that itsmagnetic field opposes the field of the holding magnet.

It will be noted that the holding magnet i8 is located in a position,axially of the coils, which is remote from the armature no. In otherwords, the magnet core iron portions 99 and 26 are next to the armature.This isolation of the holding magnet from the armature assures that theeffect of the residual magnetization of the holding magnet will not besufficiently strong to hold the armature up in case it is accidentallyknocked upward, but without completely seating the switch contacts.

The electromagnet having a magnetic circuit formed at least in part ofpermanently magnetizable material disclosed in this application iscovered by my copending application, Serial No. 218,829, filed'July 12,1938, for Electromagnet.

While I have shown a particular embodiment of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made, and I therefore contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention What I claim as new and desire toobtainby Letters Patent of the United States is:

1. The combination with a switch provided with a circuit controllingmember mounted for movement between two positions and biased to one ofsaid positions, of an operating coil for moving said member to the otherof said positions, a magnetic flux core extending axially of said coilhaving a portion formed of magnetic core iron and another portion formedof a material capable of retaining a high residual magnetic fiux forholding said member in said position, and means operated by movement ofsaid member for controlling the circuit of said operating coil.

2. The combination with a switch provided with a circuit controllingmember mounted for movement between two positions and biased to "'one ofsaid positions, of an operating coil for moving said member to the otherof said positions, a magnetic flux core extending axially of said coilhaving a portion formed of magnet core open circuit position, anarmature connected to said movable contact, a field structure providedwith a portion made of permanently magnetizable material having a highcoercive force forming a magnet for holding said armature. in a closedcircuit position, said portion being remote from said armature, anoperating coil on said field structure for moving said armature to theclosed circuit position, electrical connections for controlling theenergization of said operating coil including a switch connected withthe circuit of said operating coil so as to deenergize said coil whensaid switch is opened, and a mechanical connection between said switchand said armature for opening said switch when said armature is moved toits closed circuit position by said operating coil.

4. The combination with a switch provided with a movably mounted contactbiased to its open circuit position, an armature connected to operatesaid movable contact to its closed circuit position, a field structureprovided with a portion of permanently magnetizablematerial forming amagnet for holding said armature in said closed circuit position, anoperating coil on said field structure for moving saidarmature to saidclosed circuit position, a switch operated by said armature todeenergize said operating coil when said armature moves to said closedcircuit position,

whereupon said armature is heldby said mag-- net, a second operatingcoil on said field structure, connections for energizing said secondcoil to neutralize the eiiect of said permanent mag-.

net-and release said armature whereupon said switch opens in accordancewith its bias, a third operating coil on said field structure, andconnections for energizing said third coil in response to the current insaid switch so as to neutralize said magnet and open said switch uponthe occurrence of a predetermined current in said switch.

5. The combination with a switch provided with a movably mounted circuitcontrolling member biased to one position, an armature connected to saidcircuit controlling member, a field structure provided with a portion ofpermanently magnetizable material forming a magnet for holding saidarmature in an attracted position, an operating coil on said fieldstructure for moving said armature to said attracted position,

a relay switch biased to the open position, a coil for operating saidrelay switch to the closed position; a switch member biased to oneposition to close a circuitior said relay coil and thereby normallymaintain said-coil energized and said relay switch closed, a connectionwhereby said relay coil is energized through said relay switch aftersaid relay switch has closed, switching means for said operating coilclosed by movement of said switch member to another position, and aswitch operated by said armature for opening the circuits of said relaycoil and said operating coil.

6. .The. combination with a switch provided with a movably mountedcontact biased to its open circuit position, an armature connected tooperate saidmovable contact to its closed circuit position, afield'structure provided with a portion of permanently magnetizablematerial forming a magnet for holding said armature in said closedcircuit position, an operating coil on said field structure for movingsaid armature to said closed circuit position whereupon said oper-'.ating coil may be deenergized and said armature held in said closedcircuit position by said magnet, a second coil on said field structure,and

electrical connections for energizing said second coil in accordancewith the current in said switch so as to neutralize said magnet andthere-- by open said switch upon the occurrence of a predeterminedcurrent in said switch.

7. The combination with a switch provided with a movably mounted circuitcontrolling member biased to one position, an armature connected to saidcircuit controlling member, a field structure provided with a portion ofpermanently magnetized material forming a magnet for holding saidarmature in an attracted position, a pair of relay switches biased tothe open position, a coil for operating said relay switches to theirclosed positions, a switch member biased to one position to close acircuit for said relay coil and thereby maintain said coil energized-andsaid relay switches closed, electrical connections whereby said relaycoil is energized through one of said relay switches after said relayswitch is closed, an energizing circuit for said operating coilincluding the other one of said relay switches and switching meansclosed by movement of said CHARLES L. PERRY.

